<wicket:head>
    <style>
        div.my-tree div.wicket-tree-table-body {
            height: 20em;
            overflow: auto;
        }       
    </style>
</wicket:head>

<wicket:extend>
		<div wicket:id="feedback"></div>
		<div wicket:id="treeTable" class="my-tree">
    	</div>

</wicket:extend>